London has hundreds of commercial window cleaning companies, and on the surface many of them look similar.
The difference between a reliable long-term contractor and one that underdelivers usually comes down to what you ask before signing anything.
This checklist covers the seven questions every property manager, facilities team, and block manager should ask before appointing a commercial window cleaning contractor in London.
1. Are You Fully Insured and Can You Provide Proof?
Insurance is the first and most non-negotiable question on the list. A professional commercial window cleaning contractor should carry public liability insurance of at least £5 million, employers’ liability insurance, and; for any work involving rope access, abseiling, or at-height cleaning; specific coverage for working at height.
Employers’ liability cover of at least £5 million is a legal requirement for any contractor with employees under the Employers’ Liability (Compulsory Insurance) Act 1969.
For public liability, large corporate clients, local authorities, and building managers in London typically mandate the same minimum before appointing a contractor, so £5 million across both policies is the benchmark to look for.
Do not rely on a verbal confirmation. Ask for certificates and check that they are current. A reputable contractor will provide documentation without hesitation as part of the onboarding process.
If a company is reluctant to share insurance certificates, that tells you everything you need to know before any work begins.
At All Clean London, we carry comprehensive insurance across all services and provide full documentation to clients on request.
2. Do Your Operatives Hold IRATA Certification for Rope Access Work?
For any building above approximately seven to eight storeys where abseiling or rope access is required, IRATA (Industrial Rope Access Trade Association) certification is the industry standard. It is not enough to ask whether operatives are “trained”; ask specifically whether they hold current IRATA certification and at what level.
IRATA certification involves rigorous assessed training across three levels, with Level 1 covering supervised rope access work and Level 3 covering supervision of others.
A contractor carrying out rope access window cleaning without IRATA-certified operatives is not meeting the professional standard expected on commercial sites in London.
For a full breakdown of what IRATA and other industry accreditations mean and what to look for, our guide to commercial window cleaning accreditations covers each one in detail.
3. Are Your Operatives DBS Checked?
DBS (Disclosure and Barring Service) checks are a legal safeguarding requirement for any contractor working on school, hospital, or care home sites.
They are also increasingly expected across commercial and residential buildings where operatives may have access to communal areas, lobbies, or internal spaces.
If you manage a school or educational institution, this is non-negotiable; every operative entering the site must hold a valid enhanced DBS check before work can begin.
Our guide to school window cleaning costs in London covers the DBS requirement and other compliance considerations specific to educational settings in more detail.
At All Clean London, all operatives working on relevant sites are DBS checked as standard, and documentation is available on request.
4. What Cleaning Method Do You Use and Is It Right for My Building?
The cleaning method should be matched to the building; not simply applied based on what the contractor has available. Water-fed poles are appropriate for most buildings up to seven or eight storeys. Abseiling covers high-rise and architecturally complex buildings with no height restriction.
Cherry pickers work well on mid-rise sites with clear ground-level vehicle access. BMU and cradle systems are used on purpose-built towers where permanent access equipment is already installed.
A professional contractor will assess your building before quoting and recommend the appropriate method based on height, facade configuration, and site access; not give you a generic price before they have seen the building.
If you are not sure which method your building requires, our comparison of abseiling vs cherry picker vs water-fed pole cleaning walks through which access method is right for different building types in London.
5. Do You Use Pure Water Systems?
Pure water cleaning uses water filtered to remove all minerals and impurities, so that when it dries on the glass it leaves no residue, no streaks, and no mineral deposits.
It is the professional standard for commercial window cleaning and produces results that last significantly longer than traditional detergent-based methods.
If a contractor is using tap water and detergent on a regular commercial contract, the results will reflect that; windows will re-soil faster, streaks will be more common, and hard water deposits will build up over time.
In London, where tap water hardness is among the highest in the UK, this is a particularly relevant question.
Our guide to pure water window cleaning explains how the method works, why it produces better results on commercial buildings, and what to look for when assessing a contractor’s equipment.
6. Can You Work Around Our Building's Operating Hours?
For offices, hotels, schools, and retail buildings, cleaning during peak operating hours can cause disruption to staff, customers, and building occupants.
A professional contractor should be able to accommodate early morning, evening, or weekend cleans where required; and be transparent about whether out-of-hours scheduling incurs additional cost.
Ask specifically about how they manage access, particularly if your building requires key holder presence or has security protocols for contractors entering the site.
The best contractors will have clear processes for coordinating around your operations rather than expecting you to work around theirs.
At All Clean London, we coordinate all cleans around our clients’ operating hours and building access requirements as standard across every contract.
7. How Do You Document and Report on Cleaning Visits?
For property managers overseeing multiple buildings or reporting to managing agents, landlords, or sustainability frameworks, a documented service history is not a nice-to-have; it is essential. Ask whether the contractor provides visit confirmations, service logs, and accessible records of every clean.
Many contractors offer no documentation beyond an invoice. For commercial clients managing compliance, warranty requirements, or ESG reporting, this is a significant gap.
All Clean London’s Facade360+ platform automatically logs every clean with the date, operative records, and areas covered; giving clients a full auditable service history accessible on demand.
It is one of the features that property managers and block managers consistently cite as making contract management significantly easier.
What to Do Once You Have the Answers
Questions 1 and 2 are the baseline; if a contractor cannot answer these confidently and provide documentation, that is a red flag regardless of how competitive their pricing is.
Questions 3 to 7 help you distinguish between a contractor who is technically compliant and one who is genuinely professional, transparent, and built for a long-term working relationship.
If you are currently reviewing suppliers or appointing a commercial window cleaning contractor for the first time, our guide to hiring a window cleaning service covers the broader considerations alongside this pre-appointment checklist.
At All Clean London, we are happy to answer all seven questions before you commit to anything.
Request a free quote today and our team will provide full documentation, a site assessment, and a tailored quote for your building.
